MEXICO CITY — Mexican authorities say a mass die-off of fish at a lake in western Mexico was not due to natural causes, but the causes are still being investigated and one research said that low water levels could have been responsible.
Over 53 metric tons of rotting fish have been removed from Lake Cajititlan in western Jalisco state, the state environment department said late Sunday. Workers using shovels, a bulldozer, boats and wheel barrels removed the dead fish, which are being sent for testing. Workers wore masks to ward off the smell of rotting fish.
The small, finger-sized fish are apparently a type of chub. The cause of the die-off has not been determined; samples of the dead fish have been sent to laboratories for testing.
The state environment department said late Sunday it was not due to natural causes.
But Manuel Guzman Arroyo, director of the University of Guadalajara's Fresh Water Institute, said the lake is very shallow, and that a strong wind or other causes could have stirred up sediment and deprived the fish of oxygen.
"The lake has problems because too much water is being drawn off, and its level is very low," said Guzman Arroyo. The lake is surrounded by up-scale housing developments and its waters are used for irrigation and recreation, but he said pollution probably wasn't a big problem.
It was the fourth time this year there has been a die-off at the lake, which sits between Guadalajara and Lake Chapala.
Also Monday, authorities acknowledged that birds, turtles and fish had died off from a fuel spill at a river in the Gulf coast state of Veracruz.
The spill, which happened Aug. 27 and spread for almost a mile (1.2 kms) was caused by thieves drilling an illegal tap into a gasoline pipeline.
While workers contracted by the state-owned Pemex oil company had managed to contain the spill with booms, heavy rains had caused those containment ponds to overflow and spread the fuel again.
Dalos Rodriguez Vargas, the Veracruz state environmental prosecutor, said dozens of "reptiles, birds and fish" had been killed, but that the bigger concern was that even heavier rains could spread the pollution to a nearby lake.
"The danger is that if it rains more, with the tropical weather system out there, it could overflow again if they don't get it gathered up quickly, and reach the lake," Rodriguez Vargas said.
"They are working with all possible speed to get it contained," he said. The lake is known as the Laguna Maria Lizamaba, and is a local tourist attraction. Rodriguez Vargas said the oil company would also have to reforest the river banks where vegetation has been affected.
Thousands of illegal pipeline taps have become an increasing environmental and safety problem in Mexico, because they frequently trigger spills or explosions.
An oil spill last week in the northern state of Nuevo Leon that was also caused by an illegal tap may takes weeks to clean up, the state-run oil company said Monday.
It said some oil on the river banks was still being washed off with pressure hoses, and that cleaning up oil-soaked vegetation "will continue in the coming weeks."